Recently, progress of technique on a laser has been remarkable, and particularly, a solid state laser or semiconductor laser having an emission range of from near infrared ray to infrared ray is very useful as a light exposure source in a system wherein a printing plate precursor is directly imaged by digital data, since such laser of high powered and compact type has been easily available.
As an image recording material suitable for laser-writing, for example, a positive-working image recording material has been proposed, and such material comprises (a) a binder such as a cresol resin, (b) a compound which absorbs light so as to generate the heat, and (c) a compound such as quinonediazide which is heat-decomposable, whose pre-decomposition state being capable of substantially decreasing a solubility of said binder.
The mechanism of this material is that on IR radiation, the light-exposed area becomes alkaline-soluble, since the compound (b) generates the heat in the light-exposed area and then the compound (c) is decomposed (i.e., heat-mode type). However, the generated heat is absorbed in some degree by a substrate aluminum plate and so the thermal efficiency of this mechanism is poor, and therefore the solubility of the light-exposed area to an alkaline developing solution is not satisfactory in a development process. Consequently, alkaline strength of a developing solution must be raised to ensure the solubility of the light-exposed area.
On the other hand, in the lithographic printing plate precursor of heat-mode type, the resistance of non-heated areas (i.e., image areas) to dissolution in an alkaline developing solution is poor under the above highly alkaline concentration, and when the image recording material has slightly scratches on the surface thereof, said scratched areas may be easily dissolved. Accordingly, there is a problem such that the image areas, particularly fine line areas and the like are easily impaired. This tendency is particularly serious in a positive-working lithographic printing plate precursor employing a polymeric compound which is highly soluble to an alkaline aqueous solution.
Consequently, the raise in alkaline strength of a developing solution should be limited, though said raise in alkaline strength is intended not to leave undissolved residue on non-image areas, and it is also difficult to form a highly sharp and clear image without impairment to the formed image areas. There is therefore a need for improved sharpness and improved reproducibility of images, particularly fine images comprising a dot pattern, fine lines and the like. For the purpose of meeting the need, addition of various surfactants to a developing solution has been researched, and this attempt can attain an effect to some extent in obtaining sharpness of images.
In this connection, the use of a polyethyleneoxide adduct in an alkaline developing solution has been proposed in for example, Japanese Patent Application Publication (hereunder referred to as “J.P. KOKAI”) No. 2000-321788, and the use of a polyoxyalkylene-type nonionic surfactant in an alkaline developing solution has been proposed in for example, J.P. KOKAI No. Hei 11-338126.
However, it becomes a subject of discussion that the above compound which works as a restrainer for image areas will interact with a component in a light-sensitive layer, in particular an alkali-soluble resin, through dissolution of the component from the light-sensitive layer into the developing solution, and so the restrainer's ability to inhibit the image areas from undergoing development is decreased.